(a) Technical Field
The present invention relates to a fuel cell separator and a method for manufacturing the same. More particularly, the present invention relates to a fuel cell separator formed of a continuous carbon-fiber composite, and a method for manufacturing the same.
(b) Background Art
A fuel cell is a device that produces electricity through an electrochemical reaction of hydrogen (H2) and oxygen (O2) and includes a membrane electrode assembly (MEA) having a structure in which a fuel electrode (anode) to which hydrogen is supplied and an air electrode (cathode) to which oxygen in air is supplied are provided with an electrolyte membrane transporting hydrogen ions and that is interposed between the electrodes, and a gas diffusion layer (GDL) that is disposed on the outsides of the electrodes.
Moreover, a separator including flow fields for supplying fuel and discharging water produced by the reaction is stacked on the outside of the GDLs, thus forming a fuel cell stack in which the MEA and the separators are sequentially stacked.
Electrical energy is produced by the electrochemical reaction occurring when a fuel source such as hydrogen, or a mixed gas containing a considerable amount of hydrogen, is supplied to the fuel electrode (hydrogen electrode) on one side and oxygen, or air containing oxygen, is supplied to the air electrode (oxygen electrode) on the other side.
As shown in FIG. 4, a fuel cell separator 30 of a fuel cell stack preferably includes a plurality of manifolds 32, suitably provided at both ends of the fuel cell stack and supplying and discharging hydrogen, air, and coolant, respectively, and a plurality of hydrogen, air, and coolant flow fields 34, provided between the manifolds 32 in the longitudinal direction of the fuel cell stack, each having a fine channel structure.
The above-described fuel cell separator requires various conditions, including, but limited to, a high electrical conductivity, a high chemical resistance, a high mechanical strength, a low thermal mass (related to cold start), and the like.
Among conventional separators, since a graphite separator is formed of a thin graphite plate by a milling machine process, the manufacturing time and cost are increased and the graphite separator may further be damaged by impact.
An expansion carbon separator is difficult to form a fine channel through which a fluid flows, and the electrical conductivity is lower than that of the graphite separator.
A composite separator formed of a mixture of graphite powder and a polymer binder has difficulty in forming the fine channel for the flow of the fluid, and the electrical conductivity is lower than that of the graphite separator.
Korean Patent Application No. 10-2007-0060189 discloses a separator and a method for manufacturing the same, the method comprising mixing 75 to 85 wt % of graphite having a particle size of 10 to 200 μm, 13.5 to 22.5 wt % of phenol resin, and 1.5 to 2.5 wt % of a curing agent to prepare a composite material, dispersing the thus prepared composite material into a mold to be molded into a separator, and heat-treating the thus molded separator at a temperature of 100 to 120° C. The separator manufactured by this method is characterized by low mechanical strength and low electrical conductivity. Further, the moldability is decreased since the process of compressing the powder material in the mold is complicated. Moreover, since the time to perform the heat treatment process is substantial, the mass productivity is low.
Japanese Patent Publication No. 1999-297338 discloses a separator for a solid polymer type fuel cell using carbon/graphite powder and a polymer binder, and a manufacturing method of the same. However, the moldability of the separator described by the 1999-297338 publication is deteriorated since the process of compressing the powder material in the mold is complicated, and the mass productivity is low since the time it takes to perform the heat treatment process is substantial.
Japanese Patent Publication No. 2001-325967 discloses a manufacturing method of a fuel cell separator using a conductive powder having a grain size of 60 to 100 μm, a binder and a volatile solvent, a fuel cell separator, and a solid polymer type fuel cell. The electrical characteristics are improved when the grain content becomes high and thus the contact between the grains is increased; however if the grain content is high, the mechanical properties are decreased, and thus the moldability is decreased. Moreover, the method using the volatile solvent increases processing time, reduces work safety, and causes environmental problems.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.